Klein-Nishina Regime Research Articles

Radiation force on relativistic jets in active galactic nuclei

Radiative deceleration of relativistic jets in active galactic nuclei as the result of inverse Compton scattering of soft photons from accretion discs is discussed. The Klein-Nishina (KN) cross section is used in the calculation of the radiation force due to inverse Compton scattering. Our result shows that deceleration due to scattering in the KN regime is important only for jets starting with a bulk Lorentz factor larger than 1000. When the bulk Lorentz factor satisfies this condition, particles scattering in the Thomson regime contribute positively to the radiation force (acceleration), but those particles scattering in the KN regime are dominant and the overall effect is deceleration. In the KN limit, the drag due to Compton scattering, though less severe than in the Thomson limit, strongly constrains the bulk Lorentz factor. Most of the power from the deceleration goes into radiation and hence the ability of the jet to transport significant power (in particle kinetic energy) out of the subparsec region is severely limited. The deceleration efficiency decreases significantly if the jet contains protons and the proton to electron number density ratio satisfies the condition $n_p/n_{e0}>2\gamma_{\rm min}/\mu_p$ where $\gamma_{\rm min}$ is the minimum Lorentz factor of relativistic electrons (or positrons) in the jet frame and $\mu_p$ is the proton to electron mass ratio.

High‐Energy Emission from the TeV Blazar Markarian 501 during Multiwavelength Observations in 1996

We present the results of a multiwavelength campaign for Mrk 501 performed in 1996 March with ASCA, EGRET, Whipple, and optical telescopes. The X-ray —ux observed with ASCA was 5 times higher than the quiescent level and gradually decreased by a factor of 2 during the observation in 1996 March. In the X-ray band, a spectral break was observed around 2 keV. We report here for the —rst time the detection of high-energy c-ray —ux from Mrk 501 with EGRET with 3.5 p signi—cance (E ( 100 MeV). Higher —ux was also observed in 1996 AprilMay, with 4.0 p signi—cance for E ( 100 MeV and 5.2 p signi—cance for E ( 500 MeV. The c-ray spectrum was measured to be —atter than most of the c-ray blazars. We —nd that the multiband spectrum in 1996 is consistent with that calculated from a one-zone synchrotron self-Compton (SSC) model in which X-rays are produced via synchrotron emission and c-rays are produced via inverse Compton scattering of synchrotron photons in a homogeneous region. The —ux of TeV c-rays is consistent with the predictions of the model if the decrease of the Compton scattering cross section in the Klein-Nishina regime is considered. In the context of this model, we investigate the values of the magnetic —eld strength and the beaming factor allowed by the obser- vational results. We compare the 1996 March multiwavelength spectrum with that in the —are state in 1997 April. Between these two epochs, the TeV —ux increase is well correlated with that observed in keV range. The keV and TeV amplitudes during the 1997 April —are are accurately reproduced by a one-zone SSC model, assuming that the population of synchrotron photons in 1996 are scattered by newly injected relativistic electrons having maximum energies of However, the TeV spectrum c max D 6 ) 106. observed during the 1996 March campaign is —atter than predicted by our models. We —nd that this cannot be explained by either higher order Comptonization or the contribution of the ii seed ˇˇ IR photons from the host galaxy for the —rst-order external radiation Comptonization, but we cannot exclude possible eUects of the IR photons that may arise in the parsec-size tori postulated to exist in active galactic nuclei. Subject headings: BL Lacertae objects: individual (Markarian 501) ¨ gamma rays: observations ¨ radiation mechanisms: nonthermalX-rays: galaxies

Cut-offs and pile-ups in shock acceleration spectra

We have examined cut-offs and pile-ups due to various processes in the spectra of particles produced by shock acceleration, and found that, even in the absence of energy losses, the shape of the spectrum of accelerated particles at energies well below the nominal maximum energy depends strongly on the energy dependence of the diffusion coefficient. This has implications in many areas, for example, in fitting the observed cosmic ray spectrum with models based on power-law source spectra and rigidity dependent diffusive escape from the galaxy. With continuous energy losses, prominent pile-ups may arise, and these should be included when modelling synchrotron X-ray and inverse Compton gamma-ray spectra from a shock-accelerated electron population. We have developed a Monte Carlo/numerical technique to model the shape of the spectrum for the case of non-continuous energy losses such as inverse Compton scattering in the Klein-Nishina regime. We find that the shapes of the resulting cut-offs differ substantially from those arising from continuous processes, and we suggest that such differences could be observable through their effect on the spectrum of radiation emitted by a population of recently accelerated electrons as, for example, may exist in young supernova remnants.

Model for the High-Energy Emission from Blazars

view Abstract Citations (756) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Model for the High-Energy Emission from Blazars Dermer, Charles D. ; Schlickeiser, Reinhard Abstract Approximate formulae for the instantaneous scattered radiation spectra are derived in the Thomson and Klein-Nishina regimes, assuming that the relativistic electrons are described by an isotropic angular and power-law energy distribution in the outflowing fluid frame. The soft photon source is assumed to be axially symmetric. We find that the Thomson-limit luminosity enhancement in the direction that the scattered radiation is most intense varies as Γ6 for photons entering from the side and as Γ2 for photons entering directly from behind, where Γ is the bulk Lorentz factor of the outflowing plasma cloud. Energy loss and flow are treated in a model where energetic electrons are instantaneously injected with a power-law energy distribution at some height above a point or disk photon source, and instantaneous and time-average spectra are calculated. We also treat the electron energy-loss rate and scattered photon spectra from photon fields that are isotropic in the stationary frame. We calculate broad-band spectra for the case where soft photons are produced by a cool blackbody outer disk extending to the innermost stable orbit of a Schwarzschild black hole, and fit these results to observations of high-energy radiation from 3C 279, 3C 273, and Mrk 421. The observed spectral softening in the regime between hard X-ray and >100 MeV gamma-ray energies is attributed to the transition from an uncooled to a cooling electron distribution, yielding a break of 0.5 units in the scattered photon spectra index. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173251 Bibcode: 1993ApJ...416..458D Keywords: GALAXIES: ACTIVE; GALAXIES: JETS; GALAXIES: QUASARS: GENERAL; GAMMA RAYS: THEORY; RADIATION MECHANISMS: MISCELLANEOUS full text sources ADS | data products SIMBAD (6) NED (3)

Pair-Compton cascading in a spatially varying anisotropic radiation field

When energetic electrons Compton scatter soft photons in the Klein-Nishina regime, the produced gamma rays are subject to photon-photon pair attenuation, and a pair-Compton cascade results. We examine the formation of such cascades in the spatially varying photon fields encountered by high-energy electrons and photons emitted from luminous compact objects. Constraints on the geometry of the soft photon source and the location of the gamma-ray production site are deduced from observations of 100 MeV and TeV gamma rays emitted by galactic compact objects and active galactic nuclei.

Gamma rays from relativistic electrons undergoing Compton losses in isotropic photon fields

The kinetic equation describing Compton losses of relativistic electrons in an isotropic field of soft background photons is solved exactly including both continuous energy losses in the classical Thomson regime and catastrophic losses in the quantum Klein-Nishina regime. This extends the previous treatments of this problem, which assumed the validity of either one of these regimes alone. The problem is relevant to astrophysical sources containing relativistic electrons. Analytical solutions for the steady state electron and gamma-ray spectra in the case of power-law soft photons and monoenergetic and power-law electron injections are obtained. Numerical solutions are presented for monoenergetic, blackbody, and power-law soft photons. A comparison between the numerical and the available analytic solutions is made. 15 refs.

Saturated pair-photon cascades on isotropic background photons

view Abstract Citations (124) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Saturated Pair-Photon Cascades on Isotropic Background Photons Zdziarski, Andrzej A. Abstract The problem of high-energy gamma-rays and electrons entering an isotropic background radiation field is considered. The gamma-rays produce electron-positron pairs by photon-photon interactions with the background photons, and the electrons Compton upscatter the background photons, giving rise to a pair-photon cascade. The Compton interactions are in the quantum Klein-Nishina regime. The spectra of the secondary produced gamma-rays are obtained in the case of large optical depths of the radiation field by solving a kinetic equation of the cascade. This process can be important for the early universe, gamma-ray bursts, jets, active galactic nuclei, and ultra-high-energy gamma-rays and electrons crossing the cosmic microwave background. Publication: The Astrophysical Journal Pub Date: December 1988 DOI: 10.1086/166967 Bibcode: 1988ApJ...335..786Z Keywords: Background Radiation; Electron Photon Cascades; Electron-Positron Pairs; Elementary Particles; Gamma Ray Spectra; Black Body Radiation; Compton Effect; Electron Scattering; Radiation Distribution; Space Radiation; ELEMENTARY PARTICLES; GAMMA RAYS: GENERAL; RADIATION MECHANISMS full text sources ADS | Related Materials (1) Erratum: 1989ApJ...342.1212Z

Inverse compton emission of gamma rays near the pulsar surface

The physical conditions near pulsar surface that might give rise to gamma ray emission from Crab and Vela pulsars are not yet well understood. Here I suggest that, in the context of the vacuum discharge mechanism proposed by Ruderman and Sutherland (1975), gamma rays are produced by inverse Compton scattering of secondary electrons with the thermal radiation of the star surface as well as for curvature and synchrotron radiation. It is found that inverse Compton scattering is relevant if the neutron star surface temperature is greater than 106K or if the polar cap temperature is of the order of 5×106K. Inverse Compton scattering in anisotropic photon fields and Klein-Nishina regime is here carefully considered.